Considerable attention is given to absolute nutrient levels in lakes, rivers, and oceans, but less is paid to their relative concentrations, their nitrogen:phosphorus (N:P) stoichiometry, and the consequences of imbalanced stoichiometry. Here, we report 38 y of nutrient dynamics in Flathead Lake, a large oligotrophic lake in Montana, and its inflows. While nutrient levels were low, the lake had sustained high total N: total P ratios (TN:TP: 60 to 90:1 molar) throughout the observation period. N and P loading to the lake as well as loading N:P ratios varied considerably among years but showed no systematic long-term trend. Surprisingly, TN:TP ratios in river inflows were consistently lower than in the lake, suggesting that forms of P in riverine loading are removed preferentially to N. In-lake processes, such as differential sedimentation of P relative to N or accumulation of fixed N in excess of denitrification, likely also operate to maintain the lake’s high TN:TP ratios. Regardless of causes, the lake’s stoichiometric imbalance is manifested in P limitation of phytoplankton growth during early and midsummer, resulting in high C:P and N:P ratios in suspended particulate matter that propagate P limitation to zooplankton. Finally, the lake’s imbalanced N:P stoichiometry appears to raise the potential for aerobic methane production via metabolism of phosphonate compounds by P-limited microbes. These data highlight the importance of not only absolute N and P levels in aquatic ecosystems, but also their stoichiometric balance, and they call attention to potential management implications of high N:P ratios.

中文翻译：

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大型寡营养湖泊的持续化学计量失衡及其生态后果


人们对湖泊、河流和海洋中的绝对养分水平给予了相当多的关注，但很少关注它们的相对浓度、氮:磷 (N:P) 化学计量以及化学计量不平衡的后果。在这里，我们报告了蒙大拿州大型贫营养湖弗拉特黑德湖 (Flathead Lake) 38 年的养分动态及其流入量。虽然养分水平较低，但在整个观察期间，该湖的总氮：总磷比率（TN：TP：60至90：1摩尔）​​持续较高。湖泊的氮磷负荷以及氮磷负荷比多年来变化很大，但没有显示出系统的长期趋势。令人惊讶的是，河流入流中的 TN:TP 比率始终低于湖泊中的比率，这表明河流负荷中 P 的形式优先于 N 被去除。湖内过程，例如 P 相对于 N 的差异沉积或固定 N 的积累超过反硝化作用，也可能维持湖泊的高总氮：总磷比率。无论何种原因，该湖的化学计量失衡表现为初夏和仲夏期间浮游植物生长的磷限制，导致悬浮颗粒物中的高C:P和N:P比率，从而将磷限制传播给浮游动物。最后，该湖不平衡的氮磷化学计量似乎提高了通过限磷微生物代谢膦酸盐化合物产生需氧甲烷的潜力。这些数据不仅强调了水生生态系统中氮和磷绝对水平的重要性，还强调了它们的化学计量平衡，并提醒人们注意高氮磷比的潜在管理影响。